The subject invention discloses a method and means of tufting in which different pile heights may be obtained on conventional tufting machines by a modified yarn feed process. With more particularity, in conventional tufting, standard needles are driven through a backing layer by one of many types of needle drives to enable loops of yarn to be deposited in the backing layer and held in place by a looper positioned below the backing layer as the tufting needles withdraw. Each needle receives a single strand of yarn and the size of the loop formed will be determined by the amount of yarn fed during the tufting cycle.
Presently, two-pile height (or additional pile heights) tufting is known; however, the systems utilized for such tufting are quite complex. Typically, all yarn being delivered to the different needles is delivered by one of a number of feed rolls, each of such rolls being driven by magnetic clutches which connect each of the feed rolls to one of a number of shafts. The shafts are set to run at different speeds and thus, the feed roll speed is varied by controlling the clutches. Such machinery with large clutches and associated gears is quite cumbersome and, accordingly, patterns for the carpets are limited to a realistic number of repeats across the width of each tufted carpet.
Typically, there are ten such repeats across a standard width of carpet which means that the same pattern will be repeated in ten different places across the carpet. Since in each pattern one needle will function identically to a corresponding needle in each of the other repeats, yarns for each of these needles which produce identical patterns will be fed by a common feed roll. Thus, from any one feed roll, yarn will be fed to needles positioned across the width of the carpet. For example, if there are 1200 needles and 10 repeats, the chosen pattern would be 120 needles wide with needles Nos. 1, 121, 241, 361, 481, 601, 721, 841, 961, and 1081, all extending to the same feed roll since each of these needles represent or will tuft the first row of each of the ten repeating patterns.
It can be appreciated that the yarn strands which extend from a single feed roll to needles at different locations will be of different lengths which gives rise to tensioning problems. In present patterning machines where varying pile height capability is present, the deficiency in supplying yarn of varying tensions is partially overcome by carefully routing yarns from each feed roll to the respective needles in such a manner that the visible effect caused by the relative distance factors is minimized. Tubing commonly used for this type of routing is known as scramble tubes. Even with the use of scramble tubes, it is difficult to achieve the yarn tension control in a high-low patterning machine on the order of that achieved by a conventional non-patterning machine where the yarns can be fed directly from the feed roll to the needles without having to be routed in different directions as for example, some yarns in the two pile height patterning machine end up being routed diagonally from one end of the machine to the other.
A second detrimental aspect to present day, conventional high-low patterning is attributable to the fact that the clutch response is not instantaneous and since the distances from the feed roll may be as great as the width of the carpet, the pile height change does not occur completely until several cycles after the clutches are switched. It will be recognized that with this deficiency, the achievement of a clear pattern is difficult.
In conventional patterning high-low machines, in an effort to eliminate the difference in tension stretch in the yarns, accordingly, to produce a better defined pattern, rolls commonly known as pull rolls are utilized and located below the scramble tube bank. Presumably, all of the yarn is placed under tension in such a manner that the tension is presumably equalized. In practice, the result is far from an optimum one and weak yarns are likely to break at a weak point or a bad splice in the yarn.
Furthermore, with conventional patterning tufting machines, the limitation of a number of repeats, for example, 10, obviously limits the type of patterns which can be tufted. In machines heretofore used, there has been no commercially feasible way to control the height of each tuft of each tufting needle throughout the carpet.
Various principles utilized and some of the apparatus discussed herein are the subject matter of copending Application Ser. No. 699,905. Somewhat related subject matter is disclosed in co-pending Application Ser. Nos. 699,904 and 700,413.